The present invention relates to an aircraft having a contra-rotating dual rotor system.
Helicopters with contra-rotating rotors are known. For example:                the Piasecki H-21 helicopter has a horizontal rotor above the cabin and a second horizontal contra-rotating rotor at the tail;        the Kamov Ka-32A-12 and Ka-52 have co-axial contra-rotating rotors.        
Also, many radio controlled toy electric helicopters, such as the Heli-Max Axe Micro CX model helicopter, have co-axial contra-rotating rotors.
Contra-rotating rotors reduce the torque transmitted to the aircraft and dispenses with the need for a tail rotor. This arrangement also neutralises dissymmetry of lift during forward flight, caused by the difference in airflow over the advancing and retreating halves of the rotor blades.
However, a drawback of known co-axial contra-rotating rotor systems is the increased mechanical complexity of the rotor hub, which increases the risk of mechanical faults and failures.
The aircraft according to the present invention aims to addresses the above drawbacks by substituting a rotating rotor mast with a non-rotating rotor mast and enabling the rotor mast to tilt relative to the aircraft.
According to a second embodiment of the invention, there is provided an aircraft having a single rotor and a stator fixed against rotation on a rotor mast, wherein the orientation of the rotor mast relative to the fuselage can be varied in flight.